1. Field of the Invention
This invention relates to a gas turbine combustion apparatus.
2. Description of the Related Art
In recent years, various improvements have been made on a combustion apparatus in a gas turbine in order to decrease the concentrations of NOx (nitrogen oxides) in an exhaust gas, thereby achieving low NOx in the exhaust gas of the gas turbine. Methods in wide use for this purpose are those in which the total amount of compressed air is not introduced into a combustor, but instead, a bypass valve is provided, and part of compressed air is bypassed through the bypass valve.
As shown in FIG. 5, for example, a combustor 101 is composed of a combustor inner tube 102 and a combustor transition pipe 103. Within the combustor 101, fuel and compressed air are mixed. The fuel has been supplied from a fuel supply pipe 104 provided in a front end portion of the combustor inner tube 102, and has been injected by a fuel injection nozzle 105. The compressed air has been discharged from a compressor (not shown), passed through a diffuser 106, and introduced to an upstream side of the combustor inner tube 102. The mixed fuel and compressed air are burned in a combustion region on a downstream side of the combustor inner tube 102 or an upstream side of the combustor transition pipe 103, and introduced to a turbine stationary blade 107 as a combustion gas having a high temperature and a high pressure. In a turbine, this combustion gas is expanded to exert a driving force, which drives the compressor. The remaining output drives a generator or the like. Arrows in the drawing represent the flows of compressed air.
The ratio between the fuel and compressed air (i.e., fuel-air ratio) introduced into the combustor inner tube 102 needs to be controlled to an optimal value according to the operating state of the gas turbine (i.e., the amount of fuel charged). Thus, the whole of the compressed air is not introduced into the combustion region of the combustor 101, but part of the compressed air is bypassed and flowed into the combustor transition pipe 103 from a turbine casing chamber 109 formed from a casing 108. For this purpose, a bypass valve 110 is provided, thereby supplying part of compressed air from an opening of a bypass pipe 111 provided in the turbine casing chamber 109 into the combustor transition pipe 103. That is, the ratio between the fuel and the compressed air is controlled by the opening and closing amount of the bypass valve 110.
Such a gas turbine combustion apparatus is disclosed in Japanese Patent Publication No. 1994-48093. A combustion apparatus, in which compressed air discharged from a compressor is supplied not only into a turbine casing chamber, but is also passed through a regenerator aimed at heat exchange, and then the compressed air is supplied into the turbine casing chamber, is disclosed in Japanese Patent Application Laid-Open No. 2001-107748.
In recent years, environmental regulations have been gradually tightened, and NOx emission regulations are no exception. However, among gas turbines currently in operation, there are those whose existing facilities cannot comply with the NOx emission regulations. FIG. 6 shows a conventional gas turbine combustion apparatus which poses difficulty in decreasing NOx in an exhaust gas. In a gas turbine combustor of FIG. 6, a bypass valve 110 or the like, which controls the amount of compressed air within a turbine casing chamber 109, is not installed, so that even under a partial load, all of compressed air is introduced into a combustor 101. As a result, oversupply of compressed air occurs during combustion inside the combustor 101, producing large amounts of NOx. If it is attempted to equip this gas turbine combustion apparatus with a bypass valve 110, a bypass pipe 111 and their associated equipment intended for decreasing NOx in the exhaust gas, a space enough for the installation of ordinary bypass equipment is not present inside the turbine casing chamber, and such equipment cannot be mounted.
If there is some space within the turbine casing chamber 109, bypass equipment as shown in FIG. 7 can be installed in the gas turbine combustion apparatus of FIG. 6. However, a bypass pipe 112 would be forcibly connected to a combustor transition pipe 103 to disfigure the bypass pipe 112. This will be seen clearly when compared with the bypass pipe 111 of FIG. 5 which has been installed beforehand. A greatly curved outer site of the bypass pipe 112, and a sharply bent inner site thereof are problematical in terms of strength, and stress imposed on these sites during operation of the gas turbine combustion apparatus may result in damage.
Furthermore, the formation of such a pipe shape leads to adverse influence on the flow of compressed air passing inside the bypass pipe 112. Even if the amount of compressed air is controlled by a bypass valve 110, it would become difficult for compressed air to flow through the bypass pipe 112 into the combustor transition pipe 103, and excess compressed air within a turbine casing chamber 109 would be introduced into the combustor 101. Thus, no decrease in NOx in the exhaust gas would be obtained.